The present invention is generally directed to a system and method for amplifying a low level signal provided on electrical supply power. More specifically, the present invention is directed to a system and method for pre-amplifying an information carrying low level signal that is superimposed on electrical supply power concurrently used for energizing active components in connection with the given system. The subject system and method provide for effective amplification of the low level signal, without the undue adverse effects normally incurred in isolating the low level signal from the electrical supply power.
In certain electronic applications, a signal of interest is carried in a composite signal that also includes a power supply component. The information carrying component includes the parametric variations over time not present in the power supply component, which reflects the information being carried. In audio electronic applications, for instance, microphones having active components are often powered through the same conductive wires through which their transduced sound signals are passed. Condenser microphones whose internal components are powered via a ‘phantom power’ supply in this manner, as is often referred to in the art. The phantom power supply is a DC voltage, typically on the order of 48 volts or the like, carried on the microphone signal lines, with the time-varying audio signal itself superimposed thereon. Compared to the phantom power, the transduced audio signals tend to be relatively low in magnitude, typically on the order of several volts peak-to-peak or less.
Further downstream audio processing of the transduced audio signal requires its amplification up beyond these low levels. Because these signals are superimposed on the more significant phantom power levels, the composite received signal cannot simply be amplified and safely used downstream. The resulting voltage levels would be high enough to damage circuit components in many applications. Consequently, the conventional approach has been to separate the audio signal component of the composite signal from the phantom power component prior to any amplification or subsequent audio processing.
Several approaches have been taken in the industry for separating the information containing signal from phantom power. One often used approach is the inclusion of an AC coupling capacitor in each differential signal line, so that the non-varying component in an incoming signal on the line is filtered out, and passage of the DC phantom voltage component thereby blocked. Among the significant drawbacks of this approach are that it limits signal bandwidth and tends to introduce signal distortion.
Another often used approach is the use of transformer coupling to separate the information carrying signal from phantom power. While it is possible to preserve high signal fidelity with this approach, a sufficiently large coupling transformer is required. The prohibitively high costs of such transformers typically require design tradeoffs which accede to the limited bandwidth and unwanted signal distortion of less-than-optimal transformer coupling.
There is therefore a need for an approach for safely and effectively amplifying a low level signal component which is superimposed on electrical supply power component in an incoming signal. There is a need to so amplify such signal component to useful levels and to do so with minimal reduction in signal bandwidth and minimal signal distortion.